Landslides on Ceres

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Abstract

I analyze landslides on Ceres using several quantitative approaches to constrain the composition and structure of the top few kilometers of Ceres’ crust. I focus on a subset of archetypal landslides classified morphologically as thick, steep-snouted “type 1” (T1) flows and thin spatulate “type 2” (T2) flows (Schmidt et al., 2017) to explore the landslides’ mechanical properties, and supplement with comparison with all landslides combined. The results confirm earlier observations showing that T1 landslides are typically found poleward of 70° latitude and T2 mostly equatorward of 70° latitude. Measurements of landslide drop height and runout length imply effective friction coefficients lower than common friction coefficients in any of Ceres’ identified or suggested non-ice surface materials, including saturated clays. Measurements of the volume and area of landslide scars suggest that T1 landslides can fail to greater depths than T2 specifically and most landslides overall for a given scar area, consistent with depth-limited failure in landslides below 70° latitude. These results are consistent with a layer of lower shear strength material overlying a stronger layer in Ceres’ outer shell at low to mid latitudes, and a single layer without an overlying weak layer at polar latitudes. Combining these observations with known constraints on Ceres’ near-surface composition, I propose that Ceres’ crust at low to mid latitudes consists of a topmost layer with an ice content in excess of the near surface that thins out at high latitudes, and which overlies a somewhat stronger and more ice-rich layer.